Centrifugal pump intake pipe with a helical flow path

ABSTRACT

An intake pipe for directing a slurry towards an impeller of a centrifugal pump defines a helical flow path oriented to swirl the slurry in a rotational direction of the impeller.

FIELD OF THE INVENTION

The present invention relates to pumping of slurries, and moreparticularly to intake pipes for centrifugal pumps used to pumpslurries.

BACKGROUND OF THE INVENTION

Oil sands ores mined in Alberta, Canada are crushed and mixed withheated water, steam and caustic (NaOH) to produce slurries to beprocessed to recover bitumen. Centrifugal pumps are used tohydrotransport these oil sand slurries through pipe lines. Centrifugalpumps are also used to transport oil sands tailings through pipe lines.

Unlike single phase liquids, these slurries may contain hard, solidlumps that measure up to several inches in diameter. These lumps impactthe impeller vanes of the centrifugal pumps with high relative velocityand thereby wear or damage the impeller vanes. The repair or replacementof the impeller vanes and the associated loss of productivity is asignificant expense.

Accordingly, there is a need in the art for devices that may be used tomitigate wear or damage to impeller vanes of centrifugal pumps caused bydense slurries and larger solid particles in slurries.

SUMMARY OF THE INVENTION

In one aspect, the present invention comprises an intake pipe fordirecting a slurry towards an impeller of a centrifugal pump, whereinthe intake pipe defines a helical flow path oriented to swirl the slurryin a rotational direction of the impeller.

In another aspect, the present invention comprises a pump assembly for aslurry, the assembly comprising a volute, and an intake pipe. The volutedefines an axial pump inlet, a radial pump outlet, and a pump chamberfor an impeller rotatable about an axial impeller axis. The intake pipeis in fluid communication with the pump inlet and defines a helical flowpath oriented to swirl the slurry in a rotational direction of theimpeller. The pump inlet may be positioned to reduce the amount of thevolute that solid particles in the slurry flow through before beingdischarged at the radial pump outlet.

In another aspect, the present invention comprises a pump systemcomprising a first pump, a second pump, and an intake pipe that directsa slurry from the first pump to the impeller of the second pump, whereinthe intake pipe defines a helical flow path oriented to swirl the slurryin a rotational direction of the impeller.

In one embodiment, the intake pipe comprises a helical portion having adiameter and length, a pitch over diameter of about 2, and aneccentricity radius over diameter of about 0.2. In one embodiment, thehelical portion has a diameter of about 700 mm (28″), a length of about15,000 mm, a pitch of about 1,500 mm and an eccentricity radius of about150 mm.

With the use of a computational fluid dynamics model, it wasdemonstrated that the intake pipe of the present invention, relative toa straight intake pipe, may result in reduced wear of the impeller andthe volute of a centrifugal pump attributable to impacts between thesepump components and the larger solid particles (lumps) in the slurry.

Without restriction to a theory, it is believed that this effect is dueto the intake pipe imparting a circumferential velocity to the solidparticles in the slurry, which may reduce the impact velocity of thesolid particles with these pump components, and the amount of impactsbetween the solid particles and these pump components, and also to theintake pipe reducing the axial velocity of the solid particles prior toflowing into the centrifugal pump.

Other features will become apparent from the following detaileddescription. It should be understood, however, that the detaileddescription and the specific embodiments, while indicating preferredembodiments of the invention, are given by way of illustration only,since various changes and modifications within the spirit and scope ofthe invention will become apparent to those skilled in the art from thisdetailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring to the drawings wherein like reference numerals indicatesimilar parts throughout the several views, several aspects of thepresent invention are illustrated by way of example, and not by way oflimitation, in detail in the following figures. It is understood thatthe drawings provided herein are for illustration purposes only and arenot necessarily drawn to scale.

FIG. 1 is a perspective view of one embodiment of the intake pipe of thepresent invention.

FIG. 2 is a schematic depiction of the geometry of one embodiment of theintake pipe of the present invention.

FIG. 3 is a perspective view of one embodiment of the intake pipe of thepresent in invention, connected to one embodiment of a centrifugal pump.

FIG. 4 is a vector diagram illustrating the predicted effect of oneembodiment of the intake pipe of the present invention on the impactvelocity of a solid particle in the slurry with an impeller vane of acentrifugal pump.

FIG. 5 shows the flow path of a plurality of solid particles in a slurryflowing through one embodiment of an intake pipe of the presentinvention, and in the volute of a centrifugal pump, as predicted by acomputational fluid dynamics model.

FIG. 6 is a graph comparing the swirl velocity of a single phase fluidflowing through one embodiment of an intake pipe of the presentinvention, as predicted by a computational fluid dynamics model toexperimental results.

FIG. 7 is a graph comparing the pressure gradient of a single phasefluid flowing through one embodiment of an intake pipe of the presentinvention, as predicted by a computational fluid dynamics model, toexperimental results.

FIG. 8 is a graph comparing the average circumferential velocity ofsolid particles of a slurry flowing through embodiments of the intakepipe of the present invention having different combinations of pitchesand eccentric radii, as predicted by a computational fluid dynamicsmodel.

FIG. 9 is a graph comparing the average circumferential velocity of asingle phase fluid of a slurry flowing through embodiments of the intakepipe of the present invention having different combinations of pitchesand eccentric radii, as predicted by a computational fluid dynamicsmodel.

FIG. 10 is a graph comparing the average head loss (above that of anequivalent straight pipe) of a single phase fluid of a slurry flowingthrough embodiments of the intake pipe of the present invention havingdifferent combinations of pitches and eccentric radii, as predicted by acomputational fluid dynamics model.

FIG. 11 is a graph showing the average axial velocity of solid particlesin a slurry flowing through one embodiment of an intake pipe of thepresent invention, as predicted by a computational fluid dynamics model.

FIG. 12 shows one embodiment of the position of one embodiment of theintake pipe of the present invention relative to the impeller of acentrifugal pump, intended to increase the amount of the volute that thesolid particles of the slurry pass through before being discharged fromthe volute.

FIG. 13 shows an alternative embodiment of the position of oneembodiment of the intake pipe of the present invention relative to theimpeller of a centrifugal pump, intended to reduce the amount of thevolute that the solid particles of the slurry pass through before beingdischarged from the volute.

FIGS. 14A and 14B show the erosion of the volute of a centrifugal pumpcaused by solid particles of a slurry flowing through a straight pipeand one embodiment of an intake pipe of the present invention,respectively, as predicted by a computational fluid dynamics model.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The detailed description set forth below in connection with the appendeddrawings is intended as a description of various embodiments of thepresent invention and is not intended to represent the only embodimentscontemplated by the inventor. The detailed description includes specificdetails for the purpose of providing a comprehensive understanding ofthe present invention. However, it will be apparent to those skilled inthe art that the present invention may be practiced without thesespecific details.

The present invention relates generally to an intake pipe for acentrifugal pump. When describing the present invention, all terms notdefined herein have their common art-recognized meanings. To the extentthat the following description is of a specific embodiment or aparticular use of the invention, it is intended to be illustrative only,and not limiting of the claimed invention. The following description isintended to cover all alternatives, modifications and equivalents thatare included in the spirit and scope of the invention, as defined in theappended claims. As used herein, the term “slurry” refers to a fluidmixed with solid particles.

FIG. 1 shows one embodiment of an intake pipe 10 of the presentinvention used to supply a slurry to a centrifugal pump. In general, theintake pipe 10 comprises a pipe inlet 12, a pipe outlet 14, and ahelical portion 16. The pipe inlet 12 is for fluid communication with aslurry source. The pipe outlet 14 is for fluid communication with thepump inlet of a centrifugal pump. The helical portion 16 of the intakepipe 10 defines a helical flow path to swirl the slurry in therotational direction of the impeller of a centrifugal pump. The intakepipe 10 may be made of any rigid material suitable for conveying theslurry to a centrifugal pump, and may be formed using any suitabletechniques known in the art such as casting, molding, extrusion or acombination of the forgoing.

FIG. 2 schematically illustrates the geometry of part of the helicalportion of one embodiment of the intake pipe 10. As used herein,“longitudinal” refers to the general direction of slurry flow within thehelical portion 16 of the intake pipe 10, and “transverse” refers to adirection perpendicular to the longitudinal direction. In thisembodiment, the helical portion 16 has a circular transversecross-section C of constant diameter along the length of the intake pipe10. The geometric center of the transverse cross-section C is offsetfrom the longitudinal axis L, and revolves around the longitudinal axisL in a substantially circular path P, as the cross-section progressesalong the length of the helical portion 16, thus tracing a helical curveH. This geometry of the helical portion 16 may be quantitativelydescribed by its length, pitch and eccentricity radius. The “length”refers to the longitudinal dimension of the helical portion 16, whichwill be made up of a number of pitches. The “pitch” refers to thelongitudinal distance in which the geometric center of the transversecross-section makes one revolution around the longitudinal axis. The“eccentricity radius” refers to the transverse distance between thegeometric center of the transverse cross-section C and the longitudinalaxis L.

FIG. 3 shows one embodiment of the pump assembly 100 of the presentinvention. In general, the pump assembly 100 comprises a volute 20 of acentrifugal pump and an intake pipe 10.

The volute 20 provides a chamber in which the pressure and velocity ofthe slurry is increased by an impeller 30 rotating about an impelleraxis. As used herein, the “axial” refers to the direction defined by theimpeller axis, and “radial” refers to a direction perpendicular to theaxial direction. The volute 20 defines a pump chamber 21 for therotatable impeller 30 extending between an axial pump inlet 22, and aradial pump outlet 24. In the embodiment shown in FIG. 3, the pumpoutlet 24 discharges into a short length of discharge pipe 26 with adiffuser 28.

The intake pipe 10 is as described above in reference to FIG. 1. Thepipe outlet 14 connected to the pump inlet 22 to convey the slurry fromthe intake pipe 10 into the pump chamber 21. The helical flow path ofthe intake pipe 10 is oriented to swirl the slurry in the same directionas the rotational direction of the impeller 30 as the slurry flowstowards the pump inlet 22. In FIG. 3, for example, when viewed from thedirection from the pipe inlet 12 towards the pipe outlet 14, theimpeller 30 rotates in an anticlockwise direction, and so the helicalportion 16 also swirls the slurry in an anticlockwise direction.

FIG. 4 shows a velocity vector diagram illustrating the theoreticalprinciple of the intake pipe 10 of the present invention. The vectorV_(it) represents the tangential velocity at the leading edge of therotating impeller 30, at given moment in time. The vector V_(pa)represents the axial component of the velocity of a solid particle inthe slurry flowing towards the impeller 30. The vector V_(pt) representsthe tangential component of the velocity of the solid particle in theslurry, imparted by the swirling effect of the helical portion 16 intakepipe 10 on the slurry. The vector ΔV represents the impact velocitybetween the impeller and the solid particle of the slurry. The length ofthe vectors in FIG. 4 represent their respective magnitudes. As such,the impact velocity ΔV of the solid particle with the impeller 30 willapproach a minimum value as the tangential velocity of the solidparticle approaches the tangential velocity of the impeller 30.

Numerical Modelling of Pump System

A three-dimensional numerical computational fluid dynamics modelimplemented with the ANSYS CFX™ computational fluid dynamics softwarepackage was used to support the above theory and predict parametriceffects of different intake pipe 10 geometries. The volute 20 andimpeller 30 models were based on an commercially available high-pressurepump, with a 57.5 inch diameter impeller, 28 inch discharge pipe sectionand a 24 inch×28 inch diffuser, without any leakage flow paths. Theliquid phase of the slurry was modeled as a single continuous phasehaving a density of 1500 kg/m³ and a viscosity of 0.715 cP, which isrepresentative of an oil sands slurry comprising bitumen, sand, clay andair. Turbulence effects in the liquid phase were modeled using the k-ωSST turbulence model with scalable wall functions. The solid particlesof the slurry were modeled using discrete spherical particles having adiameter of 5 inches, accounting for drag and buoyancy forces, butignoring blockage effects. The effects of the particles on the flowfield, and inter-particle interactions were ignored.

Effect on Particle Flow Path

The model was used to predict the particle flow path in an intake pipe10 having a diameter of 28 inches, a helical portion 16 with a length of9,000 mm, pitch of 1,500 mm and eccentricity radius of 150 mm, with aslurry flow rate of 7,200 m3/hr. Of course, it is understood that othergeometries could be used depending upon a number of factors such as pumptype, pump size, etc.

FIG. 5 graphically shows, for one embodiment of the pump system 100, theflow path of a plurality of solid particles of the slurry as the slurryflows through the helical portion of the intake pipe (not shown),impacts the anticlockwise rotating impeller 30 and circulates throughpart of the volute (not shown).

As can be seen from FIG. 5, the flow paths of the solid particles have asignificant directional component that is tangential to the circularpath circumscribed by the vanes of the rotating impeller. The modelpredicts that the solid particles are mostly concentrated in aribbon-like stream which follows the helix of the undulating pipe. Inreality, the particles may not follow such a concentrated ribbon patterndue to their volume, but it would reasonably be expected that a largenumber of the solid particles would follow a predictable path governedby the geometry of the helical portion of the intake pipe 10. This isbecause the particles are expected to follow the outer surface of theinner wall of the intake pipe 10 due to the centrifugal force acting onthe particles, and the fact that the density of the particles is greaterthan the density of the slurry. If the length of straight pipe betweenthe undulating pipe and the pump inlet is kept sufficiently short, itshould be possible to control where a large portion of the particles, inparticular, the larger lumps within the slurry, e.g., greater than 10mm, will enter the pump inlet 22 and to control the tangential velocityof the larger lumps.

Effect of Eccentricity Radius and Pitch on Fluid and Solid ParticleSwirl Velocity, Fluid Pressure

The model was validated for an intake pipe 10 having a helical portionwith a pitch of 152 mm and an eccentricity radius of 17 mm usingexperimental data for a single phase fluid in a pipe of laboratoryscale. FIG. 6 is a graph comparing the predicted and experimental swirlvelocity of single phase liquid at different radial locations across thetransverse cross-section of the pipe for slurry flowing at 3 m/s. FIG. 7is graph comparing the predicted fluid pressure at different axiallocations of the intake pipe for fluids flowing at different velocities.These graphs show that the model can adequately predict the swirlvelocity and average pressure of a single phase fluid flow through anintake pipe at the laboratory scale, once the flow has fully developedin the helical portion.

With the model so validated, it was used to predict the single phasefluid pressure drop and swirl velocity generated by commercial scaleintake pipes 10 having a helical portion with six turns, and differentpitches and eccentric radii. FIG. 8, FIG. 9, and FIG. 10 are graphsshowing the predicted effect of these parameters on the averagecircumferential velocity of the solid particles, the average swirlvelocity of the single phase fluid, and the pressure of the fluid,respectively. These graphs show that the model predicts that decreasingthe pitch and increasing the eccentricity radius tends to increase thecircumferential velocity of the solid particles and fluid phase, and thepressure drop of the fluid phase. Of note, circumferential velocities ofthe particles are greater than the average circumferential fluidvelocity because the majority of the particles travel near the outsidewall of the inner surface of the intake pipe 10.

Effect of Length on Solid Particle Axial Velocity

The model was also used to predict the effect of the helical portion 16of the intake pipe 10 on the axial velocity of the solid particles foran intake pipe 10 with a helical portion having a length of 15,000 mm, apitch of 1,500 mm, and an eccentricity radius of 150 mm. FIG. 11 showsthat the average axial velocity of the solid particles varies withdistance through this geometry and eventually reaches a fairly stablevalue of 2 m/s within the undulating pipe. Upon exiting the undulatingintake pipe, it can be seen that the solid particles are thenaccelerated back to the expected average velocity of 5 m/s within thestraight pipe section. Without restriction to a theory, it is believedthat this reduction in axial velocity of the solid particles is due tothe solid particles travelling along the periphery of the pipe where theaxial velocity is lower than near the center of the pipe, and the solidparticles being decelerated by impacts with the inner wall of the intakepipe 10.

It has been noted in the field that when centrifugal slurry pumps areoperated in series, in close proximity to each other, the downstreampump will wear more quickly than the upstream pump. One proposed reasonfor this is that the particles are accelerated by the upstream pump andcarry added velocity to the downstream pump. The predicted effect of thehelical portion 16 of the intake pipe 10 in reducing the axial velocityof the solid particles may be used to mitigate the tendency of thedownstream pump in a series of pumps to wear more quickly than theupstream pump. Thus, the intake pipe 10 of the present invention may beused as an inter-stage pipe between two centrifugal pumps.

Effect of Helical Portion and Pump Inlet Position on Impeller and VoluteWear

The model was also used to qualitatively predict the effect of thehelical portion 16 of the intake pipe 10 on the wear of the impeller 30and volute of the centrifugal pump 20. The specific wear model used inthis study was that of Tabakoff-Grant. The erosion rate is calculated asper the below equations:

$E = {\lbrack {{\lbrack {1 + {k_{2}k_{12}{\sin ( \frac{\theta\pi}{2\theta_{0}} )}}} \rbrack^{2}( \frac{V_{P}}{V_{1}} )^{2}\cos^{2}{\theta ( {1 - R_{T}^{2}} )}} + ( {\frac{V_{P}}{V_{2}}{\sin (\theta)}} )^{4}} \rbrack \overset{\circ}{N}m_{p}}$where: $R_{T} = {1 - {\frac{V_{P}}{V_{3}}{\sin (\theta)}}}$

and:

k₂=1 if θ≦2θ₀

k₂=0 if θ>2θ₀

E=erosion rate (kg/s)

k₁₂, k₂=dimensionless constants

V₁, V₂, V₃=reference velocities (m/s)

V_(P)=relative velocity (m/s)

θ=impact angle (radians)

θ₀=impact angle of maximum erosion (radians)

N=number rate of particle impact on position (s⁻¹)

m_(P)=mass of particle (kg).

The specific coefficient values used in the model are outlined in Table1.

TABLE 1 Coefficient Value Units k₁₂ 5.85 × 10⁻¹ Unitless V₁ 159.11 m/sV₂ 194.75 m/s V₃ 190.5 m/s θ₀ 25 degrees

Three different configurations of pump systems were modeled: a “straightpipe”, with a pump inlet axially aligned with the impeller axis;“configuration 1” which was an intake pipe with a helical portion, witha pump; and “configuration 2”, which was also an intake pipe with ahelical portion. In configuration 1 as shown in FIG. 12, the pipe outletand pump inlet were positioned to introduce the slurry into the pumpsuch that the solid particles would travel through most of the volutebefore being discharged through the pump outlet. In contrast, inconfiguration 2 as shown in FIG. 13, the pipe outlet and pump inlet werepositioned to introduce the slurry into the pump such that the solidparticles would bypass most of the volute before being dischargedthrough the pump outlet. Each configuration was modelled for both acentrifugal pump with a volute that discharged the slurry at the bottomof the volute, and a volute that discharged the slurry at the top of thevolute.

The predicted erosion of the volute and the impeller are summarized inTable 2, below. FIGS. 14A and 14B illustrate the predicted erosionpatterns of the volute 20 of a centrifugal pump caused by solidparticles of a slurry flowing through a straight pipe and configuration2 of the intake pipe 10, respectively, both with a bottom dischargevolute.

TABLE 2 Straight Pipe-Top Discharge Total Impeller Erosion 9.71E−04 kgTotal Volute Erosion 1.67E−03 kg Straight Pipe-Bottom Discharge TotalImpeller Erosion 1.20E−03 kg Total Volute Erosion 1.66E−03 kg UndulatingPipe-Top Discharge-Config 1 Total impeller Erosion 7.85E−04 kg TotalVolute Erosion 2.32E−03 kg Undulating Pipe-Bottom Discharge-Config 1Total Impeller Erosion 6.29E−04 kg Total Volute Erosion 2.49E−03 kgUndulating Pipe-Top Discharge-Config 2 Total Impeller Erosion 8.38E−04kg Total Volute Erosion 1.22E−03 kg Undulating Pipe-BottomDischarge-Config 2 Total Impeller Erosion 5.49E−04 kg Total VoluteErosion 1.14E−03 kg Wear Reduction-Config 1 Total Impeller Erosion 19.2%Total Volute Erosion −39.4%   Wear Reduction-Config 1 Total ImpellerErosion 47.6% Total Volute Erosion −50.2%   Wear Reduction-Config 2Total Impeller Erosion 13.7% Total Volute Erosion 27.0% WearReduction-Config 2 Total Impeller Erosion 54.2% Total Volute Erosion31.6%

These results indicate that the intake pipe of the present invention mayreduce the erosion of both the volute and impeller of a centrifugalpump, relative to a straight intake pipe. Further, positioning the pipeoutlet and pump inlet to introduce the slurry into the pump such thatthe solid particles would bypass most of the volute may also beadvantageous in this regard.

Without restriction to a theory, it is believed that the reduction oferosion by using the intake pipe 10 of the present invention isattributable to a decrease in the impact velocity of solid particles inthe slurry with the leading edge of the impeller 30, as well as the factthat many of the solid particles avoid impact with the leading edge ofthe impeller 30 due to the circumferential velocity of the solidparticles imparted by the intake pipe 10.

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to those embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown herein, but is to beaccorded the full scope consistent with the claims, wherein reference toan element in the singular, such as by use of the article “a” or “an” isnot intended to mean “one and only one” unless specifically so stated,but rather “one or more”. All structural and functional equivalents tothe elements of the various embodiments described throughout thedisclosure that are known or later come to be known to those of ordinaryskill in the art are intended to be encompassed by the elements of theclaims. Moreover, nothing disclosed herein is intended to be dedicatedto the public regardless of whether such disclosure is explicitlyrecited in the claim.

We claim:
 1. An intake pipe for directing a slurry towards an impellerof a centrifugal pump, wherein the intake pipe defines a helical flowpath oriented to swirl the slurry in a rotational direction of theimpeller.
 2. The intake pipe as claimed in claim 1, wherein the intakepipe comprises a helical portion having a diameter and a length, a pitchover diameter of about 2, and an eccentricity radius over diameter ofabout 0.2.
 3. The intake pipe as claimed in claim 1, wherein the intakepipe comprises a helical portion having a length of about 15,000 mm, apitch of about 1,500 mm, and an eccentricity radius of about 150 mm. 4.The intake pipe as claimed in claim 1, wherein the intake pipe comprisesa helical portion having a length of 15,000 mm, a pitch of 1,500 mm, andan eccentricity radius of 150 mm.
 5. A pump assembly for a slurry, theassembly comprising: (a) a volute defining an axial pump inlet, a radialpump outlet, and a pump chamber for an impeller rotatable about an axialimpeller axis; and (b) an intake pipe in fluid communication with thepump inlet and defining a helical flow path oriented to swirl the slurryin a rotational direction of the impeller.
 6. The pump assembly asclaimed in claim 5, wherein the intake pipe comprises a helical portionhaving a diameter and a length, a pitch over diameter of about 2, and aneccentricity radius over diameter of about 0.2.
 7. The pump assembly asclaimed in claim 5, wherein the intake pipe comprises a helical portionhaving a length of 15,000 mm, a pitch of 1,500 mm, and an eccentricityradius of 150 mm.
 8. A pump system comprising: (a) a first pump; (b) asecond pump, wherein the second pump is a centrifugal pump comprising animpeller; and (c) an intake pipe for directing a slurry from the firstpump to the impeller of the second pump, wherein the intake pipe definesa helical flow path oriented to swirl the slurry in a rotationaldirection of the impeller.
 9. The pump assembly as claimed in claim 8,wherein the intake pipe comprises a helical portion having a diameterand a length, a pitch over diameter of about 2, and an eccentricityradius over diameter of about 0.2.
 10. The pump system as claimed inclaim 8, wherein the intake pipe comprises a helical portion having alength of 15,000 mm, a pitch of 1,500 mm, and an eccentricity radius of150 mm.